1. Field of the Invention
The present invention relates to a wiring board on which a semiconductor element is mounted, a semiconductor device in which a semiconductor element is mounted on the wiring board, and a method for manufacturing the same, and more particularly relates to a thin multilayered wiring board having excellent high-speed transmission characteristics and to a semiconductor device that uses the wiring board.
2. Description of the Related Art
Electronic devices are rapidly becoming smaller, thinner, and increasingly dense, as recently seen in mobile equipment, and greater thinness, lighter weight, higher density, and other characteristics are needed in wiring boards used in device and semiconductor element mounting due to the increase in the number of terminals that is associated with higher speeds and functionality of semiconductor elements.
Built-up boards and other boards having through-holes have conventionally been commonly used as wiring boards, but boards having through-holes are thick and are furthermore not suited to high-speed signal transmission due to the presence of through-holes.
Tape boards and other thin boards, on the other hand, are also used, but such boards cannot meet the recent demand for higher density because the methods for manufacturing tape boards limit the wiring layers to one or two layers, and the pattern positioning accuracy is inferior to built-up boards due to considerable shrinkage of the tape material.
Coreless boards have been proposed as a method for improving the problems of these wiring boards. In these boards, a wiring structure body or the like is formed on a support board that has been prepared in advance, the support board is removed or separated after the wiring structure body has been formed, and through-holes are left unformed.
The thickness of the insulating resin needs to be reduced to about 10 μm per layer in order to match the impedance of the electric circuit due to increasingly smaller wiring, and the insulating resin must have sufficient mechanical strength to be able to be thin and still be used for multilayered wiring boards. In response to these needs, a polyimide-based material, or a PBO-based (polybenzoxazole-based) material must be selected for resins having good mechanical strength and thinness as a material for the insulating resin.
Also, from the aspect of electrical characteristics and wiring design, vias with a diameter of about 10 μm are required together with the smaller wiring. Photolithography must be used in order to form vias having a diameter of about 10 μm because of the difficultly of obtaining a required shape when laser-machining or dry-etching an insulating resin.
For this reason, an insulating resin that can meet these needs requires the use of a photosensitive polyimide-based material or a PBO-based material.
Disclosed in Japanese Laid-open Patent Application No. 2000-323613 (prior art 1) is a technique in which a copper plate is used as a support board, a wiring structure is formed on the plate, and the support board is then etched away to obtain a coreless board.
Disclosed in Japanese Laid-open Patent Application No. 05-259639 (prior art 2) is a technique in which a stainless steel plate is used as a support board, a wiring structure is formed on the plate, and the support board is then peeled away to obtain a coreless board.
Disclosed in Japanese Laid-open Patent Application No. 2004-200668 (prior art 3) is a technique in which a copper foil is used as a support board, a wiring structure is formed on the foil and semiconductor elements are mounted, and the copper foil is etched to obtain a coreless board. Also disclosed in the publication is a semiconductor device in which the coreless board is used.
Disclosed in Japanese Laid-open Patent Application No. 2000-196243 (prior art 4) is a technique in which a glass board is used as a support board, a wiring structure is formed on the board, the insulation layer is abraded by laser light that is passed through the glass board, and the support board 30 is separated by exposure to pressurized steam to obtain a coreless board.
Nevertheless, the above-described methods for manufacturing the wiring boards and semiconductor devices in which a release layer is used have the following problems.
All of the prior arts 1 to 4 have structures that provided high expectations for improvements in transmission characteristics by obtaining coreless boards devoid of vias that lengthen the transmission distance, and prior arts 1 to 3 provide the necessary physical adhesive strength by roughening the surface of the insulating resin or conductor in order to ensure adhesion of the conductor on the insulating resin or the insulating resin on the conductor. Also adopted is a method for using an adhesive layer composed of chromium, titanium, tungsten, molybdenum, tantalum, vanadium, nickel, or the like in order to assure adhesive strength on the insulating resin without roughening the surface.
However, it is known that the resistance value and shape of a wiring surface have a considerable effect on the transmission characteristics as the speeds and frequencies of the semiconductor element (skin effect) become higher. For this reason, the transmission characteristics are degraded by the roughening of the surface of the insulating resin and conductor and the use of an adhesive layer composed of chromium, titanium, tungsten, molybdenum, tantalum, vanadium, nickel, or another material that has a much higher specific resistance than copper.
A photosensitive polyimide-base material and PBO material that allow vias having a diameter of about 10 μm to be formed must have a shape in which the via walls stand vertically erect because of the high resolution. Positive materials that use diazonaphthoquinone (DNQ) as a photosensitizer are excellent from the aspect of via resolution for meeting the demand for these micro-vias. However, the diazonaphthoquinone-based (DNQ-based) materials have a problem in that these materials considerably reduce the adhesion of the boundary between the insulating resin and chromium, titanium, tungsten, molybdenum, tantalum, vanadium, nickel, and other materials used in the adhesive layer and that the conductive pattern peels away because decomposition products, reaction products, and other products of the material itself are produced during heating.
In prior art 4, there is no disclosure in relation to using an adhesive layer on the wiring and roughening the surface of the insulating resin and conductor. However, since only a method for manufacturing by using CMP (Chemical Mechanical Polishing) is disclosed, it is believed that the use of a non-photosensitive resin is assumed. In particular, there is no disclosure regarding the characteristics of a photosensitive polyimide-based material in which a diazonaphthoquinone-based (DNQ-based) material is used as a photosensitizer, which is the subject matter of the present invention.